Spotify's killer feature is that you don't have to exit the app and switch to a different app to play music that they don't have.

True, there are also a few of my favorite bands on Spotify that Rdio doesn't have. Rdio seem like they haven't gotten a hold of certain indie labels. I've considered switching to a paid Spotify account just because of that.

Spotify had a terrible Android app for a while, so I switched to Rdio. Then Spotify really improved their app so I considered them again, but now Rdio's app is even better. Hmm...

Also, Rdio has a "family plan" type thing. My wife and I both have accounts, so we get a discount.

I don't take too much advantage of this because I can already find more than enough stuff to listen to there but it can be handy sometimes it's true.